The field of use of various exemplary embodiments of the present disclosure can extend to, for example, fluidic systems such as pipelines or containers through which a flow medium flows and/or in which a flow medium is kept. Both liquids such as water or chemicals or else gases such as compressed air or natural gas may be used as the flow medium.
The flow of fluids such as those in pneumatic and hydraulic systems produces flow noise. Noise can likewise be transmitted into the flow medium from the exterior via the wall of a pipeline or of a container. All these types of noise generally have characteristic properties which can depend on the way in which they are produced, and their cause can therefore be deduced by recording and analysis of such noise, by diagnosis. This makes it possible to determine a specific state of a fluidic system, in that a measured noise can be associated with a specific cause.
Fault states, such as vibration of a pipeline or fluid flowing out, can in particular be detected exactly, thus allowing state diagnosis or fault diagnosis of the system. Alternatively, either the situation in which a noise is present or is not present can be used for diagnosis purposes. For example, if flow noise occurs suddenly in a system which is normally closed, the flow noise can be diagnosed as indicating a leakage.
DE 100 02 826 A1 discloses a measurement device of this generic type for diagnosis of noise in fluidic systems. A microphone which detects noise that is present in the area of a pipeline is used to detect a leakage in the pipeline through which a pressurized flow medium is flowing. This noise is evaluated by an electronic diagnosis unit in such a way that the frequency components of flow noise, which can be distributed uniformly, and possibly the continuous noise which is can be a leakage noise, are determined and evaluated. This type of filtering makes it possible to reliably determine leakage points acoustically. Since the noise is transmitted via the fluid, the measurement of this noise can also be carried out remotely from its point of origin, thus allowing diagnosis remotely from the fault cause.
The sound signals which correspond to the noise in the fluidic system can be recorded by a structure-borne sound microphone which is fitted to the wall of the pipeline or of the container; however, more detailed measurement is possible if the microphone makes direct contact with the flow medium. The pressure fluctuations of the sound signal are thus converted quite directly, by a membrane, to mechanical oscillations of the membrane, and the mechanical oscillations are converted to electrical signals in accordance with various principles. However, due to high sensitivities of membranes, such structure-borne sound microphones can be at the same time subject to the static pressure of the flow medium which can cause failure of the microphone, such as in the event of major pressure fluctuations of the load caused by a change to the flow medium, such as when a pneumatic pressure piston is ventilated and vented. For this reason, the microphones which are of interest in conjunction various exemplary embodiments of the present disclosure make direct contact with the flow media but are configured to withstand structural failures that are common in known structure-born sound microphones. For example, as described in further detail below, exemplary embodiments of the present disclosure provide a measurement device which includes means to compensate for pressure surges of the flow medium.
U.S. Pat. No. 3,989,905 discloses a microphone with shock suppression. A membrane is arranged within a capsule in a microphone housing and converts sound waves which occur from a front face of the microphone to oscillations, and the oscillations are converted to electrical signals by a coil/magnet system. For shock suppression, an acoustic channel is provided in a microphone capsule which connects the rear face of the membrane to the front face. As a result, pressure fluctuations occur at the same time on both sides of the membrane in order not to deflect the latter or to deflect it only to a very minor extent, thus avoiding destruction.
However, the use of a microphone such as this for diagnosis of noise in fluidic systems is actually not feasible simply because of its physical form. Furthermore, miniaturization is complex, thus making installation difficult, for example, in pneumatic lines. In addition, the design does not appear to be sufficiently robust to allow it to withstand high static load changes in a hydraulic system.